1. Field of the Invention
The present invention relates to a microfilm reader/printer for projecting a microfilm image onto a screen and printing the image.
2. Description of the Related Arts
An original image recorded on a microfilm or a microfische is recorded as a vertically long image if the original is vertically long, or recorded as a laterally long image if the original is laterally long. If an image recorded on a microfilm or the like is to be merely seen in a projected form on a screen, it may be projected as it is on the screen. But when it is to be printed, it is necessary to adjust the image position for printing the image in an appropriate position on a copying paper.
To this end, on the screen there are indicated marks (hereinafter referred to as "frame marks") for determining the position of the image to be projected onto the screen for both vertically long and laterall long images. By adjusting the position of an image to be projected so that the profile of the image comes into registration with such frame marks, it is possible to print the image in a predetermined position on the copying paper.
In order to reduce the size of a printing mechanism, many microfilm reader/printers adopt a structure in which each copying paper is fed in a lateral direction, i.e., along the short sides of the copying papers and in the case of a vertically long image, the image is projected to an image forming portion without rotation of the image, while in the case of a laterally long image, the image is rotated by 90.degree. and projected to the image forming portion.
In this case, there is used an image rotating prism for turning the direction of the image projected by a projection lens, but it is difficult to obtain exact coincidence between the optical axis of the projection lens and the center of rotation of the image rotating prism, and usually there occurs a slight deviation. Consequently, the center of the projected image which has been rotated by the image rotating prism is deviated longitudinally and transversely from the center of a projected image which has not been rotated. This phenomenon is called "off-center rotation".
Thus, when an image is rotated using an image rotating prism and projected to an image forming portion, the image formed on the image forming portion is deviated longitudinally and transversely, so there arises a fear of the image being partially broken off. According to a method for preventing such partial image loss, out of the frame marks on the screen, the frame marks on the side where the image is rotated by 90.degree. at the time of printing, which frame marks correspond to the laterally long image in the foregoing example, are made smaller in size by several percents than the frame marks on the side where the image is not rotated, corresponding to the vertically long image in the foregoing example, to prevent the partial image loss even when the position of the image projected on a photosensitive drum is deviated by the off-center rotation. According to another method proposed for such purpose, the size of the frame marks for a vertically long image and that of the frame marks for a laterally long image are made equal to each other and both are set rather small to prevent the partial image loss irrespectively of whether or not the image is rotated.
Recently, a microfilm reader/printer having a zoom lens incorporated therein as the projection lens has come to be more and more popular. In this case, however, when out of frame marks provided on a screen, the size of the frame marks on the side where an image is rotated by 90.degree. at the time of printing is set smaller than the size of the frame marks on the side where the image is not rotated, it is necessary for the operator to operate the zoom lens to change the projection size and make registration of the image projected on the screen with the frame marks at every change from a vertically long image to a laterally long image on the film and at every change reverse thereto. In the case where the same frame marks are used for both vertically long and laterally long images and the size thereof is set small so as not to cause the partial image loss, it is not necessary to perform the aforesaid operation of the zoom lens, but the resulting print always involves an unnecessarily large marginal portion around the image. Since this marginal portion usually appears as a black frame, the print itself becomes very unsightly.
In conventional microfilm reader/printers, a turn-back mirror is inserted in part of a projective optical system for projecting an image onto a screen, whereby a projective image on a film is projected to a printer portion to effect printing. More specifically, a reader optical system for projection onto the screen and a printer optical system for printing have a lighting device and a projection lens in common to each other, and a turn-back mirror is inserted in the optical path portion after the projection lens to make change-over between the reader optical system and the printer optical system. As a result, the magnification of the image on the screen and that of the image to be printed out become equal to each other.
Therefore, when it is intended to obtain an enlarged image conforming to a desired size of copying paper out of various sizes of copying papers, it is necessary to adjust the projection size of the projection lens in conformity with the frame mark indicating the desired size of copying paper, but this operation is complicated. And, in effect, it has been impossible to make printing on a copying paper larger than the screen. In a certain microfilm reader/printer considering how to cope with this problem, the projection size in printing is set larger than that on a screen. More particularly, the optical path of a printer optical system is set longer than that of a reader optical system, and in addition to a turn-back mirror, a converter lens is provided removably in the optical path portion after a projection lens to thereby change a focal length (projection size). In this apparatus, the magnification ratio between the image on the screen and the image to be printed out is determined by the inserted converter lens. Therefore, for printing images on printing papers of various sizes, it is necessary to provide converter lenses for the various sizes. Further, even when converter lenses are changed from one to another according to the required size, it is necessary to make focusing at every such replacement.